Coating composition for thick coating

ABSTRACT

A coating composition for thick coating prepared by adding an aggregate to a coating liquid containing 5 to 40% by weight as SiO 2  of a coloidal silica and 3 to 40% by weight of disolved and/or finely dispersed organic polymer, having an SiO 2  /M 2  O mole ratio (in which M is a monovalent alkali metal atom) of at least 7, and having a viscosity lower than 100 c.p. at 20° C. when kept in the sealed state at 50° C. for 10 days. 
     Said coating composition being especially suitable for coating of 1-20 kg/m 2  in thickness and storable for a long period of time with an excellent stability, giving a cured coating having high water resistance, good weather resistance, high adhesive strength and no efflorescence in its surface.

This is a Divisional application of U.S. application Ser. No. 526,409,filed, Nov. 22, 1974, now U.S. Pat. No. 4,002,590, granted Jan. 11,1977.

BACKGROUND OF THE INVENTION

The present invention relates to a coating composition for forming thickcoating in amount of 1 to 20 kg/m².

In general, coating compositions for thick coating comprise a bondingagent, a dispersant or solvent, an aggregate, a pigment and otheradjuvants.

As the bonding agent, there have heretofore been used cements, organicresins, water glasses, silica sols or mixtures thereof. When water glassis used as a bonding agent for a coating composition of this type,efflorescence and reduction of the water resistance are brought aboutbased on the strong alkali of the water glass. Accordingly, use of waterglass is not preferred. On the other hand, use of an organic resin asthe bonding agent is not preferred from the practical viewpoint becauseit is expensive, the surface hardness is low in the resulting curedcoating and reduction of the water resistance is brought about in somecases. Moreover, in case a silica sol bonding agent is employed, thoughsuch advantages as prevention of occurrence of efflorescence andimprovement of the water resistance can be attained, no good adhesion isobtained in the coating composition and properties of the coatingcomposition are degraded when it is stored for a long time. Accordingly,use of a silica sol is also not preferred from the practical viewpoint.

Various composite coating liquids have heretofore been proposed ascoating liquids to overcome the foregoing defects. For instance, acomposite coating liquid comprising water glass, a silica sol and adispersion of an organic resin was disclosed in laid-opened Japanesepatent applications No. 43121/72 and No. 23833/73. However, even whensuch composite coating liquid is used for a coating composition, it isstill impossible to prevent occurrence of efflorescence on the coatedsurfaces and the defects mentioned above with respect to the coatingliquid containing a strong alkali cannot be overcome. What is moredisadvantageous is that it is very difficult to maintain an applicableviscosity over a long period of storage. Various composite coatingliquids comprising a silica sol and a dispersion of an organic resinhave heretofore been proposed, but coating compositions prepared fromsuch composite coating liquids are still insufficient in the adhesionstrength and the storage stability for a long period of time.

In general, coating compositions include so-called paints, namelycoating compositions for thin coating. In these so-called paints, thecoating amount is usually 50 to 600 g/m² and it is about 200 g/m² inmany cases. Accordingly, the problem of sagging is not serious in acoating composition of this type. Further, the solid content is lowerthan 50% in paints and it is not particularly indispensable to maintainthe viscosity at a certain high level for a long period of time. Incontrast, in the case of a coating composition for thick coating, one ofgreat objects of which being to hide convexities and concavities on asubstrate to be coated, it is important that sagging is effectivelyprevented and coating composition has such a property that anappropriate pattern can readily be formed on the coating. It isnecessary to adjust the coating composition so that a desired patterncan be obtained without sagging while the amount coated is within arange of from 1 kg/m² to 20 kg/m², generally from 2 to 5 kg/m².

SUMMARY OF THE INVENTION

It is a primary object of this invention to provide a coatingcomposition which can give a desired pattern when it is coated in anamount of 1 to 20 kg/m², the viscosity and coating characteristics ofwhich after long time storage are hardly different from those just afterpreparation.

Another object of this invention is to provide a coating composition forthick coating which can give a cured coating excellent in the waterresistance, the weather resistance and the adhesion strength withoutcausing efflorescence.

In accordance with this invention, there is provided a coatingcomposition for thick coating in an amount of 1 to 20 kg/m² containing acoating liquid which contains water and/or a hydrophilic organicsolvent, a colloidal silica and a dissolved and/or finely dispersedorganic polymer, and an aggregate, characterized in that said coatingliquid contains 5 to 40% by weight as SiO₂ of colloidal silica and 3 to40% by weight of an organic polymer, has an SiO₂ /M₂ mole ratio (inwhich M is a monovalent alkali metal atom such as Na, K and Li) of atleast 7, and has a viscosity lower than 100 c.p. at 20° C. when kept inthe sealed state at 50° C. for 10 days.

The coating liquid constituting the coating composition of thisinvention is prepared by using a silica sol having an SiO₂ /M₂ O moleratio of at least 7 and a silica component content of 10 to 50% byweight calculated as SiO₂ and including water or a hydrophilic organicsolvent as the dispersion medium and an organic polymer dispersioncontaining at least 3% by weight of an organic polymer and water or ahydrophilic organic solvent as a dispersion medium.

DETAILED DESCRIPTION OF THE INVENTION

The coating liquid having an SiO₂ concentration lower than 5% by weightis not preferred for the present invention, because the coatingcomposition including such a coating liquid as above-mentioned readilyoccurs solidification while storing and forms a cured coating having apoor strength and an insufficient weather resistance. On the other hand,when the SiO₂ concentration of the coating liquid exceeds 40% by weight,the storage stability of the coating composition including the coatingliquid is extremely poor and gelation often occurs while the coatingliquid is subjected to the stability test where it is allowed to standstill at 50° C. for 10 days.

The most preferable SiO₂ concentration of the coating liquid for thepresent invention is 7-25% by weight.

When the polymer solid concentration is lower than 3% by weight in thecoating liquid, the coating composition including the coating liquid isinsufficient in the adhesion strength and the stability. On thecontrary, when the polymer solid concentration exceeds 40% by weight, agood stability can hardly be obtained. In order for the coatingcomposition to manifest a constant pattern every time it is coated, itis indispensable that the coating composition should be stable for along time. The monovalent alkali metals such as Na, K, Li etc. may becomprised in the coating liquid used in the present invention while themole ratio of SiO₂ /M₂ O (wherein M represents a monovalent alkali metalatom) in the coating liquid should be higher than 7. The cured coatingprepared from the coating composition containing such a coating liquidthat the mole ratio of SiO₂ /M₂ O is lower than 7 exhibits efflorescencein its surface and no good water resistance. The most preferable moleratio of SiO₂ /M₂ O is in the range from 7-2,000, because coating liquidhigher than 5,000 is not so readily obtained, though higher mole ratiois preferred for this invention. The most important requirement for thecoating liquid to be used in this invention is that it has a viscositylower than 100 c.p. at 20° C. when it is kept in the sealed state at 50°C. for 10 days. Only a coating liquid satisfying this requirement cangive a coating composition which can be stored for such a long period oftime as more than 6 months. A coating composition prepared by using acoating liquid having a viscosity higher than 100 c.p. at 20° C. when itis allowed to stand still at 50° C. for 10 days in the sealed state, canonly be stored for 1 month at longest, and during the storage theworkability of the coating composition changes gradually followed by theincrease of the viscosity, and further, when such coating composition isemployed, in order to cope with expected increase of the viscosity,another recipe of the coating composition should be arranged. Morespecifically, it is necessary to reduce the content of an aggregate or afilm-forming assistant, resulting in the lowering of such properties asthe adhesion strength, the water resistance and the weather resistanceof the cured coating. In the above-mentioned stability test, it is forpreventing the change of the concentration by evaporation of thedispersion medium that the coating liquid is kept "in the sealed state".Thus the coating composition prepared by adding aggregate to such acoating liquid as just above-mentioned can be stored for a long periodof time with the excellent properties unchanged.

As is apparent from the foregoing illustration, the coating liquid to beused for formation of the coating composition of this invention ischaracterized in that 5 to 40% by weight as SiO₂ of a colloidal silicaand 3 to 40% by weight as the solids of a finely dispersed polymercomponent are contained in water or a hydrophilic organic solvent as adispersion medium, the SiO₂ /M₂ O mole ratio in the coating liquid is atleast 7, and that the coating liquid has a viscosity lower than 100 c.p.when it is allowed to stand still in the sealed state at 50° C. for 10days. Such coating liquid can easily be prepared by mixing a silica solcontaining water or a hydrophilic orgaic solvent as a dispersion mediumand having an SiO₂ /M₂ O mole ratio of at least 7 and an SiO₂concentration of at least 5% by weight with an organic polymerdispersion containing water or a hydrophilic organic solvent as adispersion medium and having an organic polymer solid concentration ofat least 3% by weight. In order to attain the objects of this invention,it is important to use a coating liquid which has a viscosity lower than100 c.p. at 20° C. when it is allowed to stand still in the sealed stateat 50° C. for 10 days. In practice, combinations a silica sol and anorgaic polymer dispersion which satisfy this stability requirement havebeen determined in advance, and a suitable combination is chosendepending on the application purpose of the coating composition.Preferred coating liquids can easily be prepared, for example, from anaqueous silica sol having an SiO₂ concentration of 35% by weight and anSiO₂ /M₂ O mole ratio of 180 and an aqueous emulsion of poly(butylacrylate) or a styrene-butyl acrylate copolymer having a polymer solidconcentration of 50% by weight, or from a water-methanol silica solhaving an SiO₂ concentration of 25% by weight and an SiO₂ /M₂ O moleratio of 120 and an aqueous emulsion of an ethylene-vinyl acetatecopolymer having a polymer solid concentration of 35% by weight.

The stability of the coating liquid is influenced by the complicatedinterfacial chemical phenomenon. More specifically, it is construed thatthe stability of the coating liquid is influenced by such factors as thedistribution of silanol groups on the surfaces of colloidal silicaparticles and the alkali ion concentration in the vicinity of thecolloidal silica particles in the silica sol and the degree of cohesionof the dissolved polymer and the interfacial chemical inter-action amongdispersed polymer particles or emulsion particles in the polymerdispersion. It is also construed that the interfacial interactionincludes a physical repellency or adsorption phenomenon and a chemicalreaction. A coating liquid having a viscosity higher than 100 c.p. atthe above-mentioned stability test has a property readily to gel andsolidify in a short time. Therefore, in such coating liquid, it isimpossible to maintain a stable dispersion state for a long period. Incontrast, a coating liquid having a viscosity lower than 100 c.p. at theabove-mentioned stability test has a high stability to long periodstorage.

The silica sol to be used for formation of the coating liquid of thecoating composition of this invention generally includes water or ahydrophilic organic solvent as a dispersion medium. As specific examplesof the dispersion medium, there can be mentioned water, alcohols such asmethanol and ethanol, polyols such as glycerin, glycol and polyalkyleneglycol, dimethylformamide, ethanolamine, quaternary ammonium hydroxidessuch as dimethyl diethanol ammonium hydroxide, nitrogen-containingcompounds such as morpholine, hydrazine and guanidine, acetone, mixturesof two or more of the foregoing organic solvents and mixtures of suchorganic solvent with water. When the SiO₂ /M₂ O mole ratio is lower than7, the majority of the silica sol forms such a solution as that fromwater glass to result in high alkali ion concentration. If such silicasol is mixed with an orlganic resin dispersion to form a coatingcomposition, the resulting composition often gells while it is allowedto stand still at 50° C. for 10 days and hence, the stability to longtime storage is very poor.

A higher SiO₂ /M₂ O mole ratio is more preferred for attaining theobjects of this invention. Even when an adjuvant containing a largeamount of alkali is added, it is possible to obtain a coating liquidcapable of attaining the objects of this invention, as far as the SiO₂/M₂ O mole ratio is maintained at a level of at least 7. As such silicasol, there are generally employed, for example, a silica sol having ahigh SiO₂ /M₂ O mole ratio, which is prepared by ion exchange methodfrom alkali silicate or peptizing silica gel in alkali, a silica solobtained by hydrolyzing an alkyl silicate such as ethyl silicate, asilica sol obtained by dissolving metallic silicon in a solution of aquaternary ammonium hydroxide, and the like. Silica sols prepared byhydrolyzing an alkyl silicate or by dissolving metallic silicon in anorganic base have an SiO₂ /M₂ O mole ratio of infinity, because they donot contain an alkali metal ion at all. Accordingly, the range of theSiO₂ /M₂ O mole ratio in the silica sol to be used for formation of thecoating composition of this invention can be expressed as from 7 toinfinity. In practice, in view of the manufacturing cost and theavailability, it is generally preferred to use a silica sol having ahigh SiO₂ /M₂ O mole ratio, which is prepared by the ion exchange methodor the peptization method. From the practical viewpoint, it isespecially preferred to use a silica sol having an SiO₂ /M₂ O mole ratioranging from 7 to about 2000. A silica sol having an SiO₂ /M₂ O moleratio exceeding 5000 is extremely difficult to prepare on an industrialscale, and hence, the manufacturing cost becomes high. The silica solhaving an SiO₂ /M₂ O mole ratio of at least 7, that is used forpreparation of the coating composition of this invention, has, ingeneral, a pH value ranging from 3 to 12. As such silica sol, there canbe mentioned, for example, aqueous silica sol, methanol silica sol,isopropanol silica sol, ethanol silica sol, acetone silica sol,water-methanol silica sol, water-isopropanol silica sol,water-tetraethanol ammonium hydroxide silica sol, and mixtures of two ormore of these silica sols. Since it is indispensable that the SiO₂concentration should be 5 to 40% by weight in the coating liquid, it isindispensable that at least 5% by weight as SiO₂ of the colloidal silicashould be contained in the silica sol. In general, it is preferred thatthe silica sol has an SiO₂ concentration of 10 to 50% by weight.

An organic polymer dispersion or solution to be used for formation ofthe coating liquid of the coating composition of this invention can beany of organic polymer dispersions customarily used for formation of theusual coating compositions or as coating materials. For example, therecan be used a polymer emulsion, a solution of a polymer in water or awater-soluble organic solvent, an aqueous dispersion of a powderypolymer, and the like. It is, however, indispensable that such organicpolymer dispersion should have a water resistant film-forming property.It is preferred that the dispersion medium is the same as the dispersionmedium used for the silica sol or has properties quite similar to thoseof the dispersion medium used for the silica sol.

As typical instances of the polymer to be used in this invention, therecan be mentioned, polyvinyl acetate, poly(methyl acrylate), poly(butylacrylate), styrene-butyl acrylate copolymers, vinyl acetate-maleic acidcopolymers, urea-formalin resins, melamine-formalin resins, naturalrubber, styrene-butadiene copolymer rubbers, acrylonitrile-butadiene,copolymer rubbers, epoxy resins, polyurethane resins and mixturesthereof.

As specific examples of the organic polymer dispersion to be used forpreparation of the coating liquid, there can be mentioned an aqueousemulsion of polyvinyl acetate, an aqueous emulsion of poly(butylacrylate), an aqueous dispersion of a styrene-butyl acrylate copolymer,an aqueous solution of a urea-formalin precondensate resin, an aqueousemulsion of a urea-melamine-formaline copolycondensate, astyrene-butadiene copolymer rubber latex, an aqueous emulsion of anepoxy resin of the bisphenol A type, and the like.

Since the polymer solids should be contained in an amount of 3 to 40% byweight in the coating liquid, it is indispensable that the organicpolymer dispersion should contain at least 3% by weight of the polymersolids.

An aggregate to be used as one constituent of the coating composition ofthis invention is chosen from mountain sand, river sand, sea sand,rocks, stones, minerals, glass, metals, inorganic solid substances andartificial aggregates. The size of the aggregate is not particularlycritical. Namely, an aggregate is optionally chosen from pulverizedmassive particles, coarse granules, powders and finely divided powders.Further, the form of the aggregate is not particularly critical, and theaggregate can take any of globular, fibrous and rod-like forms. In thisinvention, it is possible to employ any of aggregates customarily usedfor coating compositions, such as silica, alumina, calcium carbonate,asbestos, pumice, chamotte powder, vermiculite, white marble, ironoxide, titanium type pigment, chromium type pigment, etc. In addition,plastic powder, wood powder, perlite, micro glass balloon, rock wool andthe like can be used singly or in combination of the above-recitedaggregates.

Such aggregate is generally incorporated in the coating composition ofthis invention in an amount of at least 30% by weight, preferably about40% to about 80% by weight. The content of the aggregate is determineddepending on the viscosity of the coating composition, thepattern-manifesting property, the strength of the cured coating and thelike.

Any of additives can optionally be incorporated in the coatingcomposition of this invention, as far as attainment of the objects ofthis invention is not inhibited by incorporation of such additive. Assuch additive, there can be mentioned, for example, aprecipitation-preventing agent such as bentonite, magnesium silicate andclay, a leveling property-improving agent such as an alkali metal saltof polyacrylic acid, an organic polysiloxane emulsion and an ordinarysurface active agent, a water repellant such as sodium or potassiumalkyl siliconate and an emulsion of a silicone oil in which terminalgroups of an organic polysiloxane are converted to hydrophilic groups, athickener such as sodium or potassium polyacrylate,high-molecular-weight polyethylene oxide, carboxymethyl cellulose andsodium alginate, a crack-preventing agent, and the like.

In preparing the composition of this invention, the order of addition ofconstituents is not particularly critical. As a method that can beeasily practised, there can be mentioned a method comprising feedingliquid components, namely the silica sol and organic polymer dispersion,into a compounding tank provided with an agitator, mixing them in thetank, adding an adjuvant, an aggregate and the like, and agitating themixture sufficiently to form a homogeneous composition.

The coating composition of this invention is for thick coating of 1 to20 kg/m². When the amount coated is smaller than 1 kg/m², it isimpossible to manifest a desired pattern, and when the amount coated islarger than 20 kg/m², the coating material is consumed in excess andsagging readily occurs. Accordingly, it is not preferred to coat thecomposition in too small or too large an amount.

The coating composition of this invention can be used for variouspurposes. For example, it is coated for the purpose of outer or innerdecoration on the surface of concrete, slate board, calcium silicateboard, gypsum board, plywood board, metal plate or the like. It is alsoused for protection of the surface of a heat-insulating material,coating of pipes, prevention of water leakage in roof, water protectionof construction wall and other construction material, prevention ofsurface dusting in construction material and reinforcement of variousmaterials.

The coating composition of this invention can be coated according tovarious customary coating methods such as a spray coating method using aspray gun, a resin coating gun or a gun for mortar, a roller coatingmethod, a method using a curtain flow coater, and the like. A suitablecoating method is chosen depending on the purpose of coating.

Compositions of this invention and comparative compositions outside thescope of this invention will now be illustrated in more detail byreference to the following Examples.

Properties of silica sols and organic polymer dispersions used in theseExamples are shown in Table 1.

                                      Table 1.                                    __________________________________________________________________________    Silica Sols and Organic Polymer Dispersions.                                                   SiO.sub.2 /                                                                         SiO.sub.2   Solid                                                       Na.sub.2 O                                                                          Content                                                                             Disper-                                                                             Content                                    Liquid           Mole  (% by sion  (% by                                      No.  Kind of Liquid                                                                            Ratio weight)                                                                             Medium                                                                              weight)                                    __________________________________________________________________________    1.   silica sol  180   35    water --                                         2.   silica sol  120   25    water-                                                                              --                                                                      meOH*.sup.1                                      3.   acrylic emulsion*.sup.2                                                                   --    --    water 50                                         4.   acrylic emulsion*.sup.3                                                                   --    --    water 50                                         5.   ethylene-vinyl acetate                                                                    --    --    water 35                                              copolymer emulsion*.sup.4                                                6.   copolymer resin                                                                           --    --    water 50                                              emulsion*.sup.5                                                          7.   SBR emulsion*.sup.6                                                                       --    --    water 30                                         8.   polyvinyl acetate                                                                         --    --    water 40                                              emulsion                                                                 9.   urea-melamine copoly-                                                                     --    --    water 40                                              condensate emulsion*.sup.7                                               __________________________________________________________________________     *.sup.1 mixture of 60% by weight of water and 40% by weight of methanol.      *.sup.2 aqueous emulsion of polyacrylate sold and manufactured under          tradename "Movinyl 700" by Hoechst.                                           *.sup.3 aqueous emulsion of polyacrylate sold and manufactured under          tradename "A-403-2" by Showa Kobunshi.                                        *.sup.4 aqueous emulsion of ethylene-vinyl acetate copolymer sold and         manufactured under tradename "P-390" by Showa Kobunshi.                       *.sup.5 aqueous emulsion of butyl acrylate-methyl acrylatestyrene             copolymer sold and manufactured under tradename "Movinyl DM-60" by            Hoechst.                                                                      *.sup.6 aqueous emulsion of styrene-butadiene copolymer rubber.               *.sup.7 aqueous emulsion of urea-melamine-formalin precondensate.        

EXAMPLE 1

According to the recipe of coating liquid A shown in Table 2, silica solNo. 1 shown in Table 1 was first charged into a 10 l-capacitycompounding tank equipped with an agitator, then organic polymerdispersion No. 3 shown in Table 1 was added thereto little by littleunder stirring, and then water was added likewise. The resulting mixturewas still continued stirring for 10 minutes to obtain a coating liquid Ashown in Table 2. 300 g of the coating liquid A obtained just above wascharged into a 500 cc-capacity polyethylene bottle, and next the bottlewas completely sealed and was allowed to stand still in a water bathmaintained at 50° C. for 10 days. Then, the bottle was taken out of thewater bath and naturally cooled. The viscosity of the coating liquid wasmeasured at 20° C. by a viscometer of Brookfield type using the rotor ofNo. 1 at 60 r.p.m. It was found that the viscosity of the liquid was 41c.p. The viscosity of the coating liquid A had been similarly measuredjust after preparation.

According to the recipe of composition(a) shown in Table 3, 2 kg of thiscoating liquid A was mixed under agitation with bentonite, asbestospowder, silicate powder, calcium carbonate, light weight powder and anorganic thickener and agitation was still continued at room temperaturefor 3 hours in total to obtain a coating composition (a) of the presentinvention.

Each of three 2 l-capacity wide-mouthed polyethylene bottles was chargedwith 2 kg of the composition (a) prepared just above, and the viscositywas measured at 20° C. after storage of 20 days, 40 days or 60 days. Theresults are shown in Table 4, from which it is apparent that the changeof the viscosity was very small. After storage of 20 days and 40 days,the coating compositions (a) was agitated and diluted with water so thatthe viscosity was reduced to 2600 c.p. The amount of water required fordilution was shown in Table 4. A polybutylacrylate paint was coated on aslate board having a size of 20 mm×20 mm and a thickness of 6 mm and wasdried in air at room temperature for 1 day. The two coating compositions(a), each stored for 20 and 40 days and the viscosity of which wereadjusted as mentioned above, was coated in an amount of 2.5 kg/m.sup. 2on the coated surface of the slate board and the thick-coated board wasallowed to stand still at room temperature for 7 days. In order todetermine the adhesion strength, a tension was given at a rate of 1mm/min. at 25° C. in the vertical direction to the coated surface byusing a universal Tensilon tensile tester. The connecting fittings ofthe tester had been bonded to the coated surface and the back surface ofthe slate board with a two-pack type epoxy resin 1 day before themeasurement. The measurement results are shown in Table 4. It wasconfirmed that the coating composition (a) had a good storage stabilityand its adhesion strength was high and was hardly changed for a longtime.

                                      Table 2                                     __________________________________________________________________________    Recipes and Properties of Coating Liquids                                                                   Properties of Coating                                                         Liquid       Viscosity (c.p.)                                                         Polymer                                                                            at 20° C.                   Compounded Components                 Solid                                                                              Just After                         Silica Sol     Polymer Dispersion                                                                      Water        Content                                                                            after                                                                              10 days'                      Coating   Amount    Amount                                                                             Amount                                                                             SiO.sub.2 Content                                                                     (% by                                                                              prepa-                                                                             storage                       Liquid                                                                             No.  (kg) No.  (kg) (kg) (% by weight)                                                                         weight)                                                                            ration                                                                             at 50° C.              __________________________________________________________________________    A    1    2.00 3    1.00 1.00 17.5    12.5 8.2  41                            B*   1    2.00 4    1.00 1.00 17.5    12.5 7.0  320*                          C    2    2.00 5    0.50 1.50 10.0    4.4  15.0 80                            D*   2    2.00 5    0.25 1.75 10.0    2.5* 12.0 63                            E    1    2.00 6    1.00 1.00 17.5    12.5 20.0 31                            F    1    2.00 7    1.00 1.00 17.5    7.5  5.4  87                            G*   1    2.00 8    1.00 1.00 17.5    10.0 6.8  480*                          H*   1    2.00 9    1.00 1.00 17.5    10.0 7.8  3000*                         __________________________________________________________________________     *Outside the scope of the present invention.                             

                                      Table 3                                     __________________________________________________________________________    Recipes of Coating Compositions                                                               Organic*.sup.1                                                                      Bento-    Silica*.sup.2                                                                      Calcium*.sup.3                                                                      Light*.sup.4                       Coating                                                                              Coating Liquid                                                                         Thickener                                                                           nite                                                                              Asbestos                                                                            Powder                                                                             Carbonate                                                                           Weight                             Composition                                                                          Kind                                                                             Amount(g)                                                                           (g)   (g) Powder(g)                                                                           (g)  Powder(g)                                                                           Powder(g)                          __________________________________________________________________________    (a)    A  2000  10    8   20    3500 5100  20                                 (b)    B  2000  10    8   20    3500 4400  20                                 (c)    C  2000   8    8   20    3000 5000  --                                 (d)    D  2000   8    8   20    3000 5000  --                                 (e)    E  2000  10    8   20    3500 5100  20                                 (f)    F  2000  10    8   20    3500 5100  20                                 (g)    G  2000  10    8   20    3500 5100  20                                 (h)    H  2000  10    8   20    3500 5100  20                                 __________________________________________________________________________     *.sup.1 sodium polyacylate                                                    *.sup.2 95% passable through 325 mesh                                         *.sup.3 100% passable through 325 mesh                                        *.sup.4 perlite                                                          

                                      Table 4                                     __________________________________________________________________________    Properties of Coating Compositions                                                                                   Adhesion Strength                             Viscosity (c.p.) at 20° C.                                                               Amount(%) of added water*                                                                   (kg/cm.sup.2)                          Coating                                                                              Just after                                                                          After                                                                             After                                                                             After                                                                             After  After  After                                                                              After                             Composition                                                                          preparation                                                                         20 days                                                                           40 days                                                                           60 days                                                                           20 days                                                                              40 days                                                                              20 days                                                                            40 days                           __________________________________________________________________________    (a)    3200  3100                                                                              3400                                                                              3800                                                                              15     25     6.4  6.2                               (b)    2900  70000                                                                             gelled                                                                            --  60     170    1.2  0.3                               (c)    2500  2900                                                                              2800                                                                              3100                                                                              15     20     7.2  6.3                               (d)    2700  2900                                                                              2800                                                                              3200                                                                              20     40     1.0  0.8                               __________________________________________________________________________     *amount of water necessary to adjust the viscosity to 2600 c.p. (% based      on coating composition).                                                 

EXAMPLE 2

A coating liquid C shown in Table 2 was prepared in the same manner asin Example 1 by using silica sol No. 2 and polymer dispersion No. 5shown in Table 1. When the coating liquid was subjected to the stabilitytest in the same manner as in Example 1, the viscosity was 80 c.p. Acoating composition (c) shown in Table 3 was prepared in the same manneras in Example 1 by using this coating liquid.

When the coating composition was stored for a long time under the sameconditions as in Example 1, the change of the viscosity was very smallas shown in Table 4. When the adhesion strength to a slate board wastested in the same manner as in Example 1 with respect to the coatingcompositions which had been allowed to stand still for 20 days and 40days and the viscosity of which were adjusted as in Example 1, thecomposition (c) had a good stability and a high adhesion strength asshown in Table 4 even after long period storage. The coating composition(c), after allowed to stand still for 40 days, was coated on a slateboard, then dried at room temperature for 7 days. Though the board wasdipped in boiling water for 30 minutes, neither peeling of the coatingnor dusting on the surface of the coating was observed. After thisboiling water-treated coating was dried in air at room temperature for 1day, the pencil hardness was measured. It was found that it had a pencilhardness of 2 H. Thus, it was confirmed that a sufficient hardness wasmaintained in the coating and the coating has a high water resistance.

EXAMPLE 3

A coating liquid E shown in Table 2 was prepared in the same manner asin Example 1 by using silica sol No. 1 and polymer dispersion No. 6shown in Table 1. When the coating liquid E was subjected to thestability test, the viscosity was 31 c.p. Then, a coating composition(e) shown in Table 3 was prepared in the same manner as in Example 1 byusing this coating liquid E. When this coating composition was allowedto stand still at room temperature for 40 days, a slight phaseseparation was observed, but it was made homogeneous by agitation. Theviscosity of the coating composition (e) could be adjusted to 3000 c.p.by adding a small amount of water under agitation. A poly(butylacrylate) paint having a solid content of 25% was coated on a slateboard having a thickness of 3 mm by a brush and dried in air for 1 day.The coating composition (e) having its viscosity adjusted to 3000 c.p.was coated on the so obtained coated board in an amount of 1.7 kg/m² bymeans of a roller coater. A coating of a uniform pattern was obtained onthe entire surface of the board.

EXAMPLE 4

A coating liquid F shown in Table 2 was prepared in the same manner asin Example 1 by using silica sol No. 1 and polymer dispersion No. 7shown in Table 1. When this coating liquid was subjected to thestability test, the viscosity was 87 c.p. A coating composition (f) wasprepared in the same manner as in Example 1 by using the coating liquidF. Even after the coating composition (f) was allowed to stand still for40 days at room temperature, it was made homogeneous by agitation, andthe viscosity could be adjusted to 3000 c.p. by addition of only 1% ofwater. When the coating composition was subjected to the slate boardcoating test in the same manner as in Example 3, it was found that thecoating composition had a good extendable property, and it gave auniform pattern.

EXAMPLE 5

A coating composition (a) was prepared in the same manner as in Example1, and after it was stored for 40 days at room temperature, theviscosity was adjusted to 2600 c.p. and the coating test was conductedin the following manner. A poly(butyl acrylate) paint having a solidcontent of 25% was coated on a cement mortar plate by a brush, and theabove coating composition was sprayed on the coated plate under a pumppressure of 4.3 kg/cm² by using a lithium coating gun while the coatedamount of the coating composition was varied as shown in Table 5. Thestate of the coating just after spraying was examined, and the coatingwas dried at room temperature for 7 days and subjected to the waterresistance test by dipping it in boiling water for 30 minutes. Theresults are shown in Table 5, from which it will readily be understoodthat when the coating composition was thickly coated in an amount of 1.5to 5 kg/m², a good coating having an excellent water resistance wasobtained, but when it was thinly coated in an amount of 0.3 and 0.6kg/m², good coatings were not obtained.

                  Table 5                                                         ______________________________________                                        Coating Test Results                                                                                Hardness of                                                                   Coating*                                                                                Before                                                                              After                                                                   water water                                   Amount                          resist-                                                                             resist-                                 Coated               Water Resist-                                                                            ance  ance                                    (kg/m.sup.2)                                                                         State of Coating                                                                            ance Test  test  test                                    ______________________________________                                        0.3    not uniform and                                                                             partly peeled                                                                            3B    lower                                          substrate was                  than 6B                                        partly disclosed                                                       0.6      "             "        2B    "                                       1.5    beautiful pattern                                                                           not         H    HB                                             was obtained  peeled and                                                                    unchanged                                                2.5      "             "        2H    HB                                      4.0    convex and concave                                                                            "        2H    H                                              pattern of thick                                                              coating was formed                                                     5.0      "             "        2H    H                                       ______________________________________                                         *according to the pencil hardness test for paints.                       

EXAMPLE 6 (Comparison 1)

A coating liquid B shown in Table 2 was prepared in the same manner asin Example 1 by using silica sol No. 1 and polymer dispersion No. 4shown in Table 1. When the coating liquid was subjected to the stabilitytest, the viscosity was 320 c.p. A coating composition (b) was preparedin the same manner as in Example 1 by using this coating liquid B. Theviscosity of the as-prepared composition was 2900 c.p. at 20° C. but itchanged to increase the viscosity up to 70000 c.p. after 20 days'storage, and further to form a gel after 40 days storage. Further, sucha large amount of water as shown in Table 4 was required to adjust theviscosity of the coating composition (b) to 2600 c.p. after 20 days' and40 days' standing. When the adhesion strength to a slate board wastested in the same manner as in Example 1 by using the coatingcompositions (b), the viscosity of which were thus adjusted after 20days' and 40 days' standing, the adhesion strength were very low asshown in Table 4, and it was confirmed that the coating composition (b)had no practical utility when it was sotred for a long period of time.

EXAMPLE 7 (Comparison 2)

A coating liquid D shown in Table 2 was prepared in the same manner asin Example 1 by using silica sol No. 2 and polymer dispersion No. 5shown in Table 1. The polymer solid content was 2.5% by weight in theresulting coating liquid. A coating composition (d) shown in Table 3 wasprepared in the same manner as in Example 1 by using this coating liquidD. The resulting coating composition had a good storage stability. Afterthe coating compositions (d) were allowed to stand still for 20 and 40days, the viscosity was adjusted in the same manner as in Example 1, andthen the coating compositions were subjected to the adhesion test to aslate boards in the same manner as in Example 1. Only such a lowadhesion strength as shown in Table 4 was obtained, and hence, it wasconfirmed that this coating composition had no practical utility.

EXAMPLE 8 (Comparison 3)

A coating liquid G shown in Table 2 was prepared in the same manner asin Example 1 by using silica sol No. 1 and polymer dispersion No. 8shown in Table 1. When the coating liquid was subjected to the stabilitytest, the viscosity was 480 c.p. A coating composition (g) was preparedin the same manner as in Example 1 by using this coating liquid G. Whenthis coating composition was allowed to stand still at room temperaturefor 40 days, increase of the viscosity was extreme. The viscosity of thecoating composition which had been allowed to stand still for 40 dayswas adjusted to 3000 c.p. by addition of water and the composition wassubjected to the coating test in the same manner as in Example 3. Apattern was narrowly manifested, but the hardness of the dried coatingwas low and dusting was readily caused on the coating surface.

EXAMPLE 9 (Comparison 4)

A coating liquid H shown in Table 2 was prepared in the same manner asin Example 1 by using silica sol No. 1 and polymer dispersion No. 9shown in Table 1. When the coating liquid was subjected to the stabilitytest, the viscosity was 300 c.p. A coating composition (h) shown inTable 3 was prepared in the same manner as in Example 1 by using thecoating liquid H. When this composition was allowed to stand still atroom temperature for 30 days, it gelled, and even when water was addedthereto, no coating composition usable for spray coating was obtained.

What is claimed is:
 1. A coating composition for thick coating in anamount of from 1 to 20 kg/m² comprising a coating liquid containingwater, aqueous silica sol, an aqueous dispersion of an organic polymerselected from the group consisting of styrene-butyl acrylate copolymerand ethylenevinyl acetate copolymer and an aggregate, wherein saidcoating liquid contains from 5 to 40% by weight as SiO₂ of colloidalsilica, 3 to 40% by weight of said polymer, a SiO₂ /M₂ O mole ratio,wherein M is an alkali metal atom selected from the group consisting ofNa, K and Li, of from 7 to 2000 and a viscosity lower than 100 c.p. at20° C. when kept in a sealed state at 50° C. for 10 days.
 2. A coatingcomposition according to claim 1 wherein the polymer is ethylene-vinylacetate copolymer.
 3. A coating composition according to claim 1,wherein the organic polymer is styrene-butyl acrylate copolymer.